It is known to those skilled in the art that ethers, including both symmetrical and unsymmetrical ethers, may be prepared by reacting an alcohol with another alcohol to form the desired product. The reaction mixture, containing catalyst and/or condensing agent may be separated and further treated to permit attainment of the desired product. Such further treatment commonly includes one or more distillation operations.
An article titled "Expanding Refinery Technology leads to New Ether Potential," by William J Peil, Fuel Reformulation, (1992, November/December) p. 34 contains a good review of the potential of ethers other than MTBE for use in meeting the EPA's requirements.
Though MTBE is the most widely produced and discussed ether, other ethers are also being evaluated, such as diisopropyl (DIPE) and ethyl tertiary butyl ether (ETBE). DIPE can be produced from refinery propylene and water and isopropanol is an intermediate in this process. In a variation, isopropyl tertiary butyl ether could be produced by combining isobutylene with isopropanol.
The higher molecular weight ethers all have blending vapor pressures lower than MTBE, and much lower than ethanol. Their boiling temperatures are also higher than MTBE. Furthermore, higher molecular weight IPTBE and ETBE have the potential to contribute more octane. As the graph, Ibid, p. 36 illustrates, IPTBE has the capability of providing the greatest net octane increase, (R+M)/2, of all the oxygenates considered here as fuel additives to gasoline. In addition, because of their lower oxygen content, more volume of the higher MW ethers, such as IPTBE, can be added to base gasoline without exceeding the target oxygen content.
Although there has not been as much discussion regarding the production of IPTBE as there has been for MTBE, it is apparent that with its lower oxygen level and lower vapor pressure, there should be a definite niche for IPTBE in the future of reformulated gasoline.
With regard to classes of solid acid catalysts found suitable in this invention for IPTBE synthesis one of the earliest disclosures of zeolite beta was in U.S. Pat. No. 3,308,069 (1967) to Wadinger et al.
J. B. Higgins, et al. of Mobil Research and Development published an article in Zeolites, 1988, Vol. 8, November, 446-452 titled "The Framework Topology of Zeolite Beta." In the article Higgins et al. disclose what is known about the framework topology of zeolite beta. The information has been determined using a combination of model building, distance-least-square refinement and powder pattern simulation.
In an article titled "Cumene Disproportionation over Zeolite .beta. I. Comparison of Catalytic Performances and Reaction Mechanisms of Zeolites," Applied Catalysis, 77 (1991) 199-207, Tseng-Chang Tsai, Chin-Lan Ay and Ikai Wang disclose a study demonstrating that cumene disproportionation can be applied as a probe reaction for zeolite structure. It is revealed that zeolite beta would have application potential in the production of diisopropylbenzene for reasons of activity, selectivity and stability.
In a second part of the article, "II. Stability Enhancement with Silica Deposition and Steam Pretreatment", Ibid, pp. 209-222, Tsai and Wang disclose their development of two methods to improve the stability of zeolite beta, silica deposition and steam pretreatment.
Patents in the art which employ zeolite beta relate mainly to dewaxing, and cracking of hydrocarbon feedstock.
An article titled "Beta Zeolite as Catalyst or Catalyst Additive for the Production of Olefins During Cracking or Gas Oil," was written by L. Bonetto et al , 9th International Zeolite Conference, July 1992, FP 22. The authors note that with the greater demand for oxygenated compounds there is indication there might be increased demands for catalysts and conditions which maximize C.sub.3, C.sub.4 and C.sub.5 olefins. They suggest that .beta.-zeolite could be used alone or combined with Y-zeolite as a suitable zeolite component. Various catalysts were studied with respect to minimization of diffusional requirements and zeolite stability.
U.S. Pat. No. 4,419,220, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing straight chain paraffins which comprises contacting the feedstock with a .beta.-zeolite beta catalyst having a Si:Al ratio of at least 30:1 and a hydrogenation component under isomerization conditions.
Another European Application to Mobil, EP 0 094 82, discloses simultaneous catalytic hydrocracking and hydrodewaxing of hydrocarbon oils with .beta.-zeolite.
In European Patent Application 0 095 303, to Mobil, there is a disclosure of dewaxing distillate fuel oils by the use of .beta.-zeolite catalysts which, preferably have a silica:alumina ratio over 100:1. Ratios as high as 250:1 and 500:1 are disclosed as useful.
Another U.S. Pat. No. 4,518,485, to Mobil, discloses a process for dewaxing a hydrocarbon feedstock containing paraffins selected from the group of normal paraffins and slightly branched paraffins and sulfur and nitrogen compounds where, after conventionally hydrotreating the feedstock to remove sulfur and nitrogen, the hydrotreated feedstock is dewaxed by contacting the feedstock with a catalyst comprising a .beta.-zeolite having a silica/alumina ratio of at least 30:1.
In U.S. Pat. No. 4,740,292, to Mobil, there is disclosed a catalytic cracking process which comprises cracking a hydrocarbon feed in the absence of added hydrogen with a cracking catalyst comprising a .beta.-zeolite component and a faujasite component comprising at least one crystalline aluminosilicate of the faujasite structure, the weight ratio of the faujasite component to the .beta.-zeolite component being from 1:25 to 20:1.
Large pore .beta.-zeolite has been employed in the synthesis of industrially important para-cumene by toluene isopropylation. See "Toluene Isopropylation over Zeolite .beta. and Metallosilicates of MFI Structure," P. A. Parikh et al., Applied Catalysis, A, 1992, 90, p. 1.
In European Patent 323 138 and U.S. Pat. No. 4,906,787, there is disclosed a catalytic process for converting light olefins to ethers suitable as high octane blending stocks carried out by contacting the olefin, especially propene, with water and alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst. In this work diisopropyl ether (DIPE) was prepared from C.sub.3 H.sub.6 and aqueous iso-PrOH in the presence of silica-bound zeolite Beta catalyst at 166.degree..
Another European Patent, EP 323 268, light olefins are converted to alcohols and/or ethers in the presence of .beta.-zeolite.
A number of references discuss the use of faujasite zeolites in various applications.
Japanese Patent 82-07432 teaches the use of zeolites, particularly mordenites and faujasites, to make dialkyl ethers containing primary or secondary alkyl groups by the liquid phase dehydration of alcohols.
U.S. Pat. No. 4,058,576 to Chang et al. teaches the use of (pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a pore size greater than 5 angstrom units and a silica-to-alumina ratio of at least 12, to convert lower alcohols to a mixture of ethers and olefins.
In allowed U.S. patent application Ser. No. 07/917,218, there is disclosed a method for preparing methyl tertiary butyl ether by reacting butanol and methanol in the presence of a catalyst comprising a super-acid alumina or a faujasite-type zeolite.
In U.S. Pat. No. 5,081,318, a Y-type zeolite modified with fluorosulfonic acid is disclosed.
In U.S. Pat. No. 3,955,939, to Sommer et al. (1976), there is disclosed the production of a water-free mixture of isopropyl alcohol, diisopropyl alcohol, diisopropyl ether and by-products by the catalytic hydration of propylene in the gaseous phase at temperatures of 140.degree.-170.degree. C., wherein the water-free mixture formed according to the process can be used directly as an additive to gasoline fuel.
None of the available references would seem to suggest the conversion of the acetone portion present in a by-product stream into IPTBE. The portion of said by-product stream which typically comprises acetone is about 10% to 80%. It would greatly enhance the economics of any process to produce oxygenates if acetone from a by-product stream could be converted to useful oxygenate products such as isopropyl tertiary butyl ether, as well as methyl tertiary butyl ether (MTBE).